Pressure Release Valve Research Articles

Intragenic suppression of gain-of-function mutations in the Escherichia coli mechanosensitive channel, MscL.

Mechanosensitive channels play an important role in protecting bacterial cells from osmotic downshock by serving as biological 'pressure release valves'. One of these channels, MscL, is found throughout the bacterial kingdom, but has been most studied in Escherichia coli. The E. coli MscL is a 136-amino-acid protein organized as a homopentamer with each subunit containing two transmembrane segments. Previous studies have shown that several residues, including V23 and G26, are essential for normal function of MscL; very severe gain-of-function phenotypes in which cell growth slows or is arrested can result from residue substitutions at these positions. Through random mutagenesis and growth selection, we have generated intragenic suppressors of the V23A and G26S mutations. The suppressor mutants have been characterized by growth phenotype, Western blot and patch clamp. Most of the mutations that render phenotypic suppression are located in the transmembrane domains with additional sites lying in the periplasmic loop. In contrast, only one mutation is found in the amino-terminal S1 domain, and none is found within the carboxyl-terminal domain. Not only have these findings revealed functional domains and subdomains critical for MscL function, but they also predict a pair of residues that interact directly during channel opening.

Evaluation of a new cuff pressure release valve

Evaluation of a new cuff pressure release valve

Laboratory Evaluation of the Limitations of Positive Pressure Safety Valves on Hard-Shell Venous Reservoirs

Vacuum-assisted venous drainage (VAVD) is a technique used to increase venous return during cardiopulmonary bypass (CPB). However, VAVD has created some new safety concerns. One potential problem is the pressurization of the venous reservoir in the event of vacuum failure. To prevent this overpressurization, a positive pressure release valve (PPRV) is placed on the venous reservoir. The purpose of this study was to determine if there is a difference in the pressurization of venous reservoirs using various PPRVs. The method of this study included evaluation of four different venous reservoirs and their associated PPRVs. Each reservoir was completely sealed, and two roller pumps with 1⁄4-in tubing were connected to the reservoir suction inlet. The roller pumps were calibrated, and a disposable pressure transducer was used to measure pressure at the venous inlet. Each reservoir was first sealed and then pressurized to test the occlusion of the roller heads. The PPRVs were tested by measuring the venous inlet pressure at a range of suction flow rates from 0–5 L/min. Linear regression analysis was performed to predict the venous inlet pressure from the rate of suction flow for each PPRV. The PPRV in the Baxter, Gish, and Gambro reservoirs maintained a low reservoir pressure (<40 mmHg) even at excessive suction flow rates (3–5 L/min). The PPRV in the Medtronic reservoir allowed excessive pressures (>40 mmHg) even at low flow rates (1–2 L/min). It is recommended that any reservoir used for VAVD be evaluated in a similar manner to determine whether it is safe under the maximal suction and vent flow conditions possible during clinical practice.

A constant humidity air supply system for pilot scale applications

This paper outlines the development of an apparatus to supply air with both controlled temperature and relative humidity, at a variety of flow rates up to 114 L min−1. To achieve adjustable constant relative humidities in the air, the two-pressure principle was used. This method involved saturating the air at a higher pressure, and then passing the air through a pressure release valve to the lower working pressure to achieve the desired humidity, while controlling the temperature to the desired level. The absolute pressure when the saturation is achieved determines the humidity of the final air. Standard design procedures were followed to ensure the air approached saturation in the pressurized column and that the amount of water was sufficient to make sure the columns would not run out of water during an experiment. The problems encountered included a pressure fluctuation coming from the compressor through the pressure regulator, and a regular fluctuation in the temperature of the water, within a 90 min period, when the water temperature was used to control the air temperature exiting the column. These problems were overcome by using two-pressure regulators on the air supply and by controlling the temperature of the water rather than the air temperature. The result was a stable but adjustable temperature and relative humidity air supply.

Survey of intussusception reduction in England, Scotland and Wales: How and why we could do better

AIM: The aim of our study was to assess the variation in technique among hospitals in England, Wales and Scotland. In addition, local in hospital variation among paediatric radiologists at our own institution was assessed. METHOD: Postal questionnaires were distributed to the radiology departments of 301 hospitals. RESULTS: 183 (60.8%) replies were received. 122 institutions reduced intussusceptions and 61 did not. A lack of paediatric surgical and/or anaesthetic cover, and a lack of radiological experience were the major reasons cited by the departments which did not attempt intussusception reduction. Sixty-five hospitals use barium for hydrostatic reduction, 43 employ pneumatic reduction, 10 use water-soluble enemas and four use ultrasound. Of the 65 centres using barium 16 (25%) reported a success rate of less than 50%,24 (37%) had a 50–70% success rate, seven (11%) reduce greater than 70% of intussusceptions and 18 (27%) did not know. In the 43 institutions employing air reduction, one (2%) had a success rate less than 50%, 20 (47%) had a 50–70% success rate, 17 (40%) a success rate greater than 70% and five (11%) did not know. Overall, of the total number of hospitals which replied to our survey, 28 (23%) reported that they were not aware of their success rates. Within the pneumatic reduction group in particular there was marked variation in the methods and duration of attempted reduction - between different hospitals and within the same institution. In six departments the machine used for pneumatic reduction did not measure intraluminal pressure. CONCLUSIONS: Ultrasound is underutilized despite being a sensitive method in diagnosis. There is almost certainly an over-reliance on plain radiographs and on the use of sedation, antibiotics and anti-spasmodics in general. We believe a 70% or greater success rate should be achievable in most institutions whether by pneumatic or hydrostatic reduction, and all departments should strive to achieve success rates in this range. Less than a quarter of centres who replied currently achieve this standard. Successful reduction rates below 50% are unacceptable in our opinion. Not surprisingly, success rates are generally highest in those centres treating more than 20 cases per annum. Twenty-eight (23%) of hospitals performing intussusception reductions did not know their success rates. Regular audits of intussesception figures should take place in all institutions. Unacceptably wide variations in intussusception reduction techniques currently exist. An accurate pressure release valve at least, and preferably intraluminal pressure monitoring should be an integral component of all pneumatic reduction devices. The British Paediatric Radiology and Imaging Group or the Royal College of Radiology should address these issues and introduce some standardization of practice.

The construction of a chamber for nitrogen fumigation

Abstract The design and construction of a nitrogen fumigation chamber with a pressure release valve is described. After several modifications due to excessive leakage it is now possible to use that constructed to perform two‐week fumigations of museum objects at 0.3% oxygen in a 1.8m3 capacity chamber using three cylinders of nitrogen. Steel, an oxygen impermeable material, was used for the panels of the chamber but there is still some apparent leakage. As this leakage probably occurs at joins in the panels, a simpler design, ie, with no extension tube, would probably have been better. A halogen leak detector was indispensable for detecting the site of leaks but the rate of use of gas was a better indication of the extent of leakage. A gas bubbler also indicated pressure failure in the chamber when gas flowed from the cylinder but escaped through leaks. The chamber complements the main pest eradication technique of freezing.

Oxygen flow through nasal cannulae.

Since many operating theatres do not have distinct oxygen flowmeters, flow rates of oxygen were measured via nasal prongs at several settings and attachments to three anaesthetic machines. Oxygen-flow rates were measured using a Timeter RT-200 Calibration Analyzer at three, five and eight L.min-1 via nasal prongs attached to a distinct flowmeter, the common gas outlet (CGO) and the Y-piece of a circle system with the adjustable pressure release (APL) valve closed, open and partially open at circuit pressures of 10 and 20 cm H2O. The most accurate delivery of oxygen from a distinct flowmeter and the CGO (mean difference 0.2 +/- 0.2 and 0.4 +/- 0.4 respectively). Differences between the flowmeter and CGO were not significant (P = 0.1). Accuracy of flows via the Y-piece were worse than via the flowmeter and CGO (P < 0.0001). Flows via the Y-piece were less than those dialed, especially at high rates. With a partially open APL valve, flow depended upon pressure in the anaesthetic circuit, not upon the flow set. With the APL valve completely open, no flow occurred. To deliver supplemental oxygen in the operating theatre when there are no distinct flowmeters, nasal prongs should be attached to the CGO of the anaesthetic machine or a flowmeter on a portable E-tank oxygen cylinder. Connecting nasal prongs to the Y-piece of a circle system should be avoided since oxygen delivery is less than dialed, especially when the APL valve is open.

Vacuum Erection Associated Impotence and Peyronie's Disease

Purpose Use of a nonmedical, catalogue type vacuum erection device resulted in a case of vacuum induced vasculogenic impotence and Peyronie's disease. Materials and Methods A 66-year-old potent man used a nonmedical vacuum erection device (cylinder plus a hand pump without a pressure-release valve and a doughnut-shaped ring at the base without tension bands) after having achieved a spontaneous rigid erection. The resultant excessive overinflation of the penis was followed by dorsal curvature, diminished rigidity and decreased erectile maintenance. Results Physical examination revealed a dorsal mid shaft Peyronie's plaque. Nocturnal penile tumescence testing and office injection testing were abnormal and demonstrated partial, shortlived, dorsally curved erections. Dynamic pharmaco-cavernosometry and pharmaco-cavernosography established vasculogenic impotence with site-specific crural (unrelated to the Peyronie's plaque) veno-occlusive dysfunction and dorsal penile curvature. Conclusions Vacuum erection devices create pulling forces on the penis. We estimate that the pulling forces in this case were prohibitively high (approximately 29 pounds) due to absence of a pressure-release valve and to the preexistent erection at vacuum application. These intense pulling forces are hypothesized to have damaged the tunica in the mid shaft (Peyronie's disease) and the crus (veno-occlusive dysfunction), the latter being the site of attachment of the corpora to the ischiopubic ramus and a most likely location for high magnitude pulling forces to exert an abnormal injury effect. The patient underwent a Nesbit plication procedure and presently performs self-injection for satisfactory sexual activity.

Pneumatic audio sweep generator

A pneumatic sweep generator for use as an audio source in tests near vocal frequency ranges. A horn, whose volume may be controlled by air pressure and whose tone may be controlled by air velocity, is connected to an air supply in a dual-circuit arrangement. Mechanical control devices, such as manual and pressure release valves, are located within the circuit to provide for tone and volume control. A reciprocating air cylinder continuously varies the air velocity within the horn to sweep the frequencies in an adjustable manner. Electromagnetic interference is totally eliminated by a complete absence of electrical devices in either the device or in necessary controls.

Holding tank for waste fluids and process for disposing of waste fluids from recreational vehicles

An in-ground holding tank to collect sewage and grey water from recreational vehicles in areas where central sewer facilities are not feasible. The holding tank has a typical volume of 60-100 gallons and is made of non-corrosive material. The tank contains input and removal assemblies, a pressure release valve, and may contain a volume gauge.

Capillary Pressure Techniques: Application to Exploration and Development Geology

Capillary pressure can be viewed as the pressure required to drive a fluid through a pore throat and displace the pore wetting fluid, with greater pressure being required as the pore throat becomes smaller. The size and distribution of pore throats within a host rock control its capillary pressure characteristics, which in turn control fluid behavior in the pore system. Mercury-injection capillary pressure curves, which measure capillarity, are obtained by injecting mercury into sample plugs to produce a plot of injection pressure vs. mercury saturation. The resulting capillary pressure curves can provide qualitative assessments of reservoir rock using such calculated values as pore-throat sorting, reservoir grade, and oil columns required to obtain 50 and 75% oil saturat ons. Regional capillary pressure maps of these calculated values identify a north-south trend of favorable reservoir rock along the state line between Montana and North Dakota in the third porosity (C) zone of the Ordovician Red River Formation. Oil migration and trapping can be significantly controlled by capillary pressure. At Bell Creek field, in southeastern Montana, multiple oil-water contacts in Cretaceous Muddy Sandstone barrier sands can be explained with the concept of a capillary pressure release valve. Semi-permeable siltstones can only trap finite columns with the excess oil being released updip to migrate into other reservoir quality sand bodies. Oil columns can be estimated from capillary pressure data by determining the buoyancy force of the oil floating on water and the converting from a mercury-air capillary system to an oil-water capillary system. Relative permeability data may also be calculated from capillary pressure data and can be used to estimate fractional water production at given water saturations. Tilted oil-water contacts can result from hydrodynamics, capillary pressure, or both, and capillary pressure data can help determine the type of tilting present. By understanding capillarity, we can obtain better insight on the nature of reservoir rock, oil accumulations, and permeability relationships.

Use of pressure release valve to prevent colonic injury during colonoscopy

Although bowel perforation during colonoscopy is often related to direct endoscopic pressure or injury in the rectosigmoid area, colonic perforation has been also reported with overinflation of air. This latter type of rupture appears related to formation of a blind loop, to an overly competent ileocecal valve that prohibits colonic decompression, or to use of particular power sources that generate unsafe pressure levels. In an effort to obviate this pneumatic type of rupture, the authors tested a pressure release valve developed by the Olympus Corporation that supplants the standard air-water valve in available Olympus colonoscopes. Use of this valve revealed a significant difference in mean and maximal intracolonic pressures generated during colonoscopy. Moreover, its use resulted in a marked decrease in tissue damage in the pneumatically inflated cadaver colon. Incorporation of such a pressure release valve into available colonoscopes should reduce the risk of pneumatic colon rupture and improve the safety of diagnostic colonoscopy.

A Device for Determining the Concentration of Formation Treating Acids

Published in Petroleum Transactions, AIME, Volume 204, 1955, pages 273–274. Some of the problems associated with the acid treatment of oil wells are related to the control of the composition of formation treating acid. One test usually made at the well site is the determination of the acid concentration. Heretofore, the concentration of the acid delivered to the well site usually has been interpreted from a hydrometer measurement of the specific gravity of the acid solution. Experience has shown that this indirect measurement of acid concentration can give erroneous results. More reliable results are, of course, obtainable by the titration method; however, this method is not easily adapted to well-site testing. To overcome these objections, a device was developed for use in the field which permits determination of the concentration of treating acid both quickly and accurately at the time of the acid treatment. Its purpose was three-fold, namely, to determine:the concentration of the fresh treating acid,the concentration of the spent acid returning from the well, andthe solubility of formation samples in treating acid. The device was designed to operate on the principle of the stoichiometric relation between the calcium carbonate-hydrochloric acid reaction and the carbon dioxide gas resulting from the reaction. By confining the carbon dioxide gas within a reaction cell of the type shown in Fig. 1, the pressure inside the cell is increased. Since the pressure is an indication of the quantity of carbon dioxide gas produced, it may be used to estimate the concentration of the acid, provided an excess of calcium carbonate is used. From information on the volume of the reaction cell, the volume of acid used, and the pressure and temperature of the gas after the completion of the reaction, the concentration of the treating acid may be computed. The reaction cell is essentially a pressure vessel equipped with a pressure gage, temperature indicator, pressure release valve, and a special sample holder. Plastic and metal construction makes the cell both rugged and acid-resistant.